feat(telemetry): Add Tempo search filters for the path-finding attributes

This branch emits nine pathfind attributes and the datasource offered a dropdown
for none of them, so the signal was there but not searchable in Explore. The
file's own header states that each phase adds filters for what it introduces.

Six filters, for the attributes that select a request. The three counts are
measurements read off a span rather than things an operator searches by, so they
get none. ledger_index is dynamic because it takes a new value every ledger.

docker/telemetry/grafana/provisioning/datasources/tempo.yaml

@@ -7,6 +7,7 @@
 # Each phase adds filters for the span attributes it introduces.
 # Base filters — node identity, service, span name, status.
 # RPC command, status, role filters.
+# Path-finding request, mode and ledger filters.
 
 apiVersion: 1
 
@@ -106,3 +107,38 @@ datasources:
             operator: "="
             scope: span
             type: dynamic
+          # Path-finding filters. Only the attributes that select a request get
+          # a dropdown; pathfind_num_paths, pathfind_num_requests and
+          # pathfind_num_source_assets are measurements read off a span, not
+          # things an operator searches by.
+          - id: pathfind-source-account
+            tag: pathfind_source_account
+            operator: "="
+            scope: span
+            type: dynamic
+          - id: pathfind-dest-account
+            tag: pathfind_dest_account
+            operator: "="
+            scope: span
+            type: dynamic
+          - id: pathfind-dest-currency
+            tag: pathfind_dest_currency
+            operator: "="
+            scope: span
+            type: dynamic
+          - id: pathfind-fast
+            tag: pathfind_fast
+            operator: "="
+            scope: span
+            type: dynamic
+          # Changes every ledger, so it must be dynamic rather than static.
+          - id: pathfind-ledger-index
+            tag: pathfind_ledger_index
+            operator: "="
+            scope: span
+            type: dynamic
+          - id: pathfind-search-level
+            tag: pathfind_search_level
+            operator: ">"
+            scope: span
+            type: dynamic